Device for coating the inner surfaces



3,126,300 BULBS March 24, 1964 J. BIENEFELT ETAL DEVICE FOR COATING THE INNER SURFACES 0F FOR INCANDESCENT LAMPS AND DISCHARGE TUBES WITH A POWDER Filed Aug. 50, 1961 ELECTRODE F IG.2

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INVENTOR JACOBUS BIENE FELT HENRICUS A.VAN BAKEL AGE United States Patent 3,126,300 DEVICE FOR COATING THE INNER SURFACES 0F BULBS FOR INCANDESCENT LAMPS AND DISCHARGE TUBES WITH A POWDER Jacobus Bienefelt and Henricus Antonius van Bakel,

Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y.,, a corporation of Delaware Filed Aug. 30, 1961, Ser. No. 134,880 Claims priority, application Netherlands Sept. 2, 1960 3 Claims. (Cl. 118-49.1)

This invention relates to devices for coating the inner surfaces of bulbs for incandescent and discharge tubes with a powder. Such a device comprises a member for holding a bulb, a nozzle to be introduced into the neck of the bulb, which carries a first electrode and has one or more channels adapted to be connected to a powder supply, and a second electrode arranged externally of the bulb and exhibiting a potential difference relative to the first electrode, means also being provided for heating the bulb to be coated. Such a device is known and is used, for example, in electrostatically coating the inner surfaces of bulbs for incandescent lamps with a thin layer of powder consisting substantially of SiO In the electrostatic coating process, an amount of finely-divided siO -powder is blown into the bulb to be treated, the wall of which has been made sufficiently conductive by heating. Due to the presence of electrodes of different potentials, arranged one on each side of the bulb surface to be coated, the finely-divided powder blown into the bulb is drawn towards the wall and expanded over the surface thereof. After this process, the adhesion between the powder and the bulb wall may be improved in the usual manner, for example by means of a treatment with vapour.

One of the problems involved in the internal coating of bulbs is how to supply the finely-divided powder to the bulb wall so as to cover this wall very uniformly.

According to the present invention, it is possible to meet the requirement of high uniformity of coating by utilizing a device which is characterized in that of at least a number of the channels in the nozzle, the main directions of at least those parts of the channels which lie near the outlet apertures for the powder are convergent in the direction of spraying, since it has been found that, as compared with known devices in which all of the channels in the nozzle extend co-axially with the axis of the neck of the bulb, the SiO -powder is surprisingly distributed over the bulb wall much more uniformly if channels of parts of channels in the nozzle are convergent in the indicated manner. The relevant channels are preferably directed towards the axis of the neck of the bulb to be coated.

As a rule, the nozzle is also provided with a plurality of drilled channels. It is not necessary for all of the channels in the nozzle to be convergent in the direction of spraying.

In another embodiment of the invention, for technical reasons of manufacture, the center lines of at least the convergent channels in the nozzle are located on a conical peripheral surface.

In a particular embodiment of the invention, the nozzle has a conical annular slot which is preferably adjustable. This embodiment affords the advantage of a greater continuity, as reckoned over the periphery of the slot, in the supply of powder. This supply may be increased or decreased at will because of the adjustability of the slot.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

FIGURE 1 shows an arrangement of the principal elements required for the electrostatic coating of bulbs. FIGURE 2 shows the nozzle of the device of FIGURE 1, which has convergent channels in accordance with the invention. FIGURE 3 is a plan view of the nozzle of FIGURE 2. FIGURE 4 shows a nozzle in which the channels in the nozzle of FIGURE 2 are united into a conical slot.

The device shown in FIGURE 1 comprises a frame 1 in which a disc 4, provided with a V-shaped groove 3 and bearing on a plurality of balls 5, is rotatably arranged. The disc 4 may be set into rotation via a rope transmission 6 by means of an electric motor (not shown). A bulb holder 9 is secured to the disc 4 with the interposition of a part 8 of insulating material. A circular spring 12 is arranged in horizontal tangential slots of the holder 9 so as to clamp in position a bulb, placed in the holder, at three areas.

There is also provided a device for the supply of finelydivided powder to the wall of the bulb, which device is movable in a vertical direction relative to the frame 1 and the bulb holder 9 and is to be inserted into the neck of a bulb 10. The said device comprises two co-axial tubes 15 and 16. The tube 15 has at its upper end a nozzle 18, which merges into a pointed part 11 and is formed as an electrode. A plurality of convergent channels 19 are drilled in the nozzle 18. A flow of a gas, such as air, in which an amount of SiO -powder having a particle size of preferably at most millimicrons is distributed with great fineness, may be led through the tube 15 and through the channels 19 to the interior of the bulb in the direction indicated by an arrow 17. The excess powder is drawn away in the direction indicated by an arrow 20 via the space between the tubes 15 and 16 by means of a suction device, otherwise not shown.

A stationary burner 25, formed as a positive electrode and connected through three separately-adjustable connections to a common gas supply 26, is arranged externally of the bulb. A bulb 10 placed in the rotary holder 9 may be heated by the burner device 25 for the purpose of making the bulb wall to be coated of better electric conductivity.

The inner surface of the bulb 10 may now be electrostatically coated with a powder by providing a potential difference of, say, 15,000 volts direct voltage between the nozzle 18, formed as a negative electrode, and the burner 25, formed as a positive electrode. The powder supplied in the direction indicated by the arrow 17, after having left the nozzle through the channels 19, is drawn towards the surface of the bulb and expanded over this surface. A thin layer of powder once having been applied to the wall, the adhesion between the powder and the wall may be improved, if necessary, by means of a treatment with vapor.

The uniformity of the coating with SiO -powder is considerably enhanced, as has surprisingly been found, by utilizing in accordance with the invention a nozzle 29 screwed into the end of the inner tube 15 (FIGURE 2). Such a nozzle has a plurality of channels positioned in a special way. In the plan view of FIGURE 3, the channels are positioned along a circumference. The channels, only two of which are shown in FIGURE 2 and indicated there by 30 and 31, are drilled into the nozzle so that their main directions 35 and 36 form the surface of a cone which, in this example, has an apical angle of 30. It has been found that the introduction of a nozzle with channels convergent in the direction of spraying provides a considerable improvement in uniformity of the layer thickness of the coated bulbs.

The embodiment shown in FIGURE 4 comprises a nozzle having two relatively adjustable parts 37 and 38 which are the boundaries of an annular conical slot 39.

An annular part 41, connected by means of ridges 40 to the part 38, is screwed into the part 37. Several bores 42 are provided at the upper side of the inner part 38 to permit the annular part 41 to be screwed into the outer part 37. As compared to drilled channels, a greater continuity in the powder supply may be obtained by using a nozzle with a conical slot as shown in FIGURE 4.

What is claimed is:

1. In a device for coating the inner surfaces of bulbs for incandescent lamps and discharge tubes with a powder, having members for holding a bulb which is to be coated, a nozzle having at least two channels adapted to be connected to a fine powder supply in a gas above atmospheric pressure which nozzle is provided with a first electrode adapted to be introduced into the neck of a bulb, and a second electrode arranged externally along the outer surface of the bulb and exhibiting a potential difference relative to the first electrode for coating the inner surfaces of said bulbs, means also for heating the bulb to be coated, the combination comprising at least a number of the channels in the nozzle each having an outflow aperture for said fine powder, the main directions of at least those parts of the channels which lie near the outflow apertures for the powder being convergent in the direction of spraying.

2. In a device as claimed in claim 1, wherein the center lines of at least parts of the convergent channels are located on a conical peripheral surface.

3. In a device as claimed in claim 2, wherein the nozzle has an adjustable conical annular slot.

References Cited in the file of this patent UNITED STATES PATENTS 2,566,392 Wilkins et a1. Sept. 4, 1951 2,785,926 Lataste Mar. 19, 1957 2,806,444 Werner et al. Sept. 17, 1957 3,045,925 Giangualano July 24, 1962 

1. IN A DEVICE FOR COATING THE INNER SURFACES OF BULBS FOR INCANDESCENT LAMPS AND DISCHARGE TUBES WITH A POWDER, HAVING MEMBERS FOR HOLDING A BULB WHICH IS TO BE COATED, A NOZZLE HAVING AT LEAST TWO CHANNELS ADAPTED TO BE CONNECTED TO A FINE POWDER SUPPLY IN A GAS ABOVE ATMOSPHERIC PRESSURE WHICH NOZZLE IS PROVIDED WITH A FIRST ELECTRODE ADAPTED TO BE INTRODUCED INTO THE NECK OF A BULB, AND A SECOND ELECTRODE ARRANGED EXTERNALLY ALONG THE OUTER SURFACE OF THE BULB AND EXHIBITING A POTENTIAL DIFFERENCE RELATIVE TO THE FIRST ELECTRODE FOR COATING THE BULB TO BE COATED, THE COMBINATION COMPRISING AT LEAST A NUMBER OF THE CHANNELS IN THE NOZZLE EACH HAVING AN OUTFLOW APERTURE FOR SAID FINE POWDER, THE MAIN DIRECTIONS OF AT LEAST THOSE PARTS OF THE CHANNELS WHICH LIE NEAR THE OUTFLOW APERATURES FOR THE POWDER BEING CONVERGENT IN THE DIRECTION OF SPRAYING. 